1. Field of the Invention
The present invention relates a retractable photographic lens which can retract to make the length thereof shorter than that in a ready-to-photograph state when no photographic operation is carried out.
2. Description of the Related Art
Miniaturization of cameras is ever continuous, and therefore, miniaturization of retractable photographic lenses for cameras, which retract to reduce the length thereof in a non-operating state, has been in increasing demand. As a solution to meet this demand, the assignee of the present invention has proposed a retractable lens which is disclosed in U.S. Pat. No. 6,978,089 (U.S. patent application Ser. No. 10/368,342). This retractable lens is characterized in that a plurality of optical elements of a photographing optical system are aligned with an optical axis in a ready-to-photograph state, and that a part of the plurality of optical elements is radially-retracted to a position (radially-retracted position) deviating from the optical axis of the remaining optical elements while being retracted, together with remaining optical elements on the optical axis thereof, in the direction of the optical axis of the photographing optical system when the photographic lens is fully retracted.
The retractable optical element disclosed in U.S. Pat. No. 6,978,089 not only moves forward and rearward along a photographing optical axis in a similar manner as to a movable optical element of a conventional zoom lens, but also moves radially about a pivot parallel to the photographing optical axis. Therefore, the retractable optical element is required to move with a high degree of accuracy. In this case, it is a matter of course to position the retractable optical element precisely on the photographing optical axis, and it is desirable to control the position of the retractable optical element also in a state where the retractable optical element is retracted from the photographing optical axis. For instance, if the radially-retracted position of the retractable optical element is controlled with a high degree of precision, it is not necessary to provide an excessive clearance for the movement of the retractable optical element in anticipation of positional errors occurring when the retractable optical element is moved to the radially-retracted position, which makes it possible to further miniaturize the photographic lens.